Shock absorber having a continuously variable valve with base line valving

ABSTRACT

A shock absorber includes an external control valve which controls the damping characteristics of the shock absorber. The external control valve controls the flow of fluid between the lower working chamber of the shock absorber and the reservoir chamber and between the upper working chamber of the shock absorber. The damping characteristics are dependent on the amount of current being applied to a solenoid valve which controls a fluid valve assembly. A soft fluid valve assembly is disposed in series with the fluid valve assembly to allow for the tuning of the damping forces at low current levels provided to the solenoid valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/787,452 filed on Apr. 16, 2007. The entire disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to a hydraulic damper or shock absorberadapted for use in a suspension system such as the suspension systemsused for automotive vehicles. More particularly, the present disclosurerelates to a hydraulic damper or shock absorber having an externallymounted electromagnetic control valve with soft valving which generatesdifferent pressure-flow characteristics as a function of the currentsupplied to the electromagnetic control valve.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

A conventional hydraulic damper or shock absorber comprises a cylinderwhich is adapted at one end for attachment to the sprung or unsprungmass of a vehicle. A piston is slidably disposed within the cylinderwith the piston separating the interior of the cylinder into two fluidchambers. A piston rod is connected to the piston and extends out of oneend of the cylinder where it is adapted for attachment to the other ofthe sprung or unsprung mass of the vehicle. A first valving system istypically incorporated within the piston functions during the shockabsorber's extension stroke of the piston with respect to the cylinderto create a damping load. A second valving system typically incorporatedwithin the piston in a mono-tube design and in the base valve assemblyin a dual-tube design functions during the shock absorber's compressionstroke of the piston with respect to the cylinder to create a dampingload.

Various types of adjustment mechanisms have been developed to generatedamping forces in relation to the speed and/or amplitude of thedisplacement of the sprung or unsprung mass. These adjustment mechanismshave mainly been developed to provide a relatively small or low dampingcharacteristic during the normal steady state running of the vehicle anda relatively large or high damping characteristic during vehiclemaneuvers requiring extended suspension movements. The normal steadystate running of the vehicle is accompanied by small or fine vibrationsof the unsprung mass of the vehicle and thus the need for a soft ride orlow damping characteristic of the suspension system to isolate thesprung mass from these small vibrations. During a turning or brakingmaneuver, as an example, the sprung mass of the vehicle will attempt toundergo a relatively slow and/or large movement or vibration which thenrequires a firm ride or high damping characteristic of the suspensionsystem to support the sprung mass and provide stable handlingcharacteristics to the vehicle. These adjustable mechanisms for thedamping rates of a shock absorber offer the advantage of a smooth steadystate ride by isolating the high frequency/small amplitude excitationsfrom the unsprung mass while still providing the necessary damping orfirm ride for the suspension system during vehicle maneuvers causing lowfrequency/large excitations of the sprung mass. Often, these dampingcharacteristics are controlled by an externally mounted control valve.An externally mounted control valve is advantageous in that it may beeasily removed for service or replacement.

The continued development of shock absorbers includes the development ofadjustment systems which provide the vehicle designer with acontinuously variable system which can be specifically tailored to avehicle to provide a specified amount of damping in relation to variousmonitored conditions of the vehicle and its suspension system.

SUMMARY

A shock absorber according to the present disclosure includes a pressuretube defining a working chamber. A piston is slidably disposed on thepressure tube within the working chamber and the piston divides theworking chamber into an upper working chamber and a lower workingchamber. A reserve tube surrounds the pressure tube to define a reservechamber. An intermediate tube is disposed between the reserve tube andthe pressure tube to define an intermediate chamber. An external controlvalve is secured to the reserve tube and the intermediate tube. An inletto the control valve is in communication with the intermediate chamberand an outlet of the control valve is in communication with the reservechamber. The control valve generates different pressure flowcharacteristics for the damper or shock absorber which controls thedamping characteristics for the damper or shock absorber. The differentpressure-flow characteristics are a function of the current supplied tothe control valve.

The external control valve also includes the ability to tune the softdamping characteristics for the shock absorber. The soft damping allowsfor the tuning of the damping forces at low current levels provided tothe control valve over the complete velocity range of the shockabsorber.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 illustrates an automotive vehicle which incorporates shockabsorbers in accordance with the present disclosure;

FIG. 2 is a cross-sectional side view of one of the shock absorbersillustrated in FIG. 1;

FIG. 3 is an enlarged cross-sectional side view of the externallymounted control valve illustrated in FIG. 2; and

FIG. 4 is an enlarged cross-sectional side view of an externally mountedcontrol valve in accordance with another embodiment of the disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.Referring now to the drawings in which like reference numerals designatelike components throughout the several views, there is shown in FIG. 1 avehicle incorporating a suspension system having shock absorbers inaccordance with the present disclosure, and which is designated by thereference numeral 10.

Vehicle 10 includes a rear suspension 12, a front suspension 14 and abody 16. Rear suspension 12 has a transversely extending rear axleassembly (not shown) adapted to operatively support a pair of rearwheels 18. The rear axle is attached to body 16 by means of a pair ofshock absorbers 20 and by a pair of springs 22. Similarly, frontsuspension 14 includes a transversely extending front axle assembly (notshown) to operatively support a pair of front wheels 24. The front axleassembly is attached to body 16 by means of a pair of shock absorbers 26and by a pair of springs 28. Shock absorbers 20 and 26 serve to dampenthe relative motion of the unsprung portion (i.e., front and rearsuspensions 12, 14) with respect to the sprung portion (i.e., body 16)of vehicle 10. While vehicle 10 has been depicted as a passenger carhaving front and rear axle assemblies, shock absorbers 20 and 26 may beused with other types of vehicles or in other types of applicationsincluding, but not limited to, vehicles incorporating non-independentfront and/or non-independent rear suspensions, vehicles incorporatingindependent front and/or independent rear suspensions or othersuspension systems known in the art. Further, the term “shock absorber”as used herein is meant to refer to dampers in general and thus willinclude McPherson struts and other damper designs known in the art.

Referring now to FIG. 2, shock absorber 20 is shown in greater detail.While FIG. 2 illustrates only shock absorber 20, it is to be understoodthat shock absorber 26 also includes the control valve design describedbelow for shock absorber 20. Shock absorber 26 only differs from shockabsorber 20 in the manner in which it is adapted to be connected to thesprung and unsprung masses of vehicle 10. Shock absorber 20 comprises apressure tube 30, a piston assembly 32, a piston rod 34, a reserve tube36, a base valve assembly 38, an intermediate tube 40 and an externallymounted control valve 42.

Pressure tube 30 defines a working chamber 44. Piston assembly 32 isslidably disposed within pressure tube 30 and divides working chamber 44into an upper working chamber 46 and a lower working chamber 48. A sealis disposed between piston assembly 32 and pressure tube 30 to permitsliding movement of piston assembly 32 with respect to pressure tube 30without generating undue frictional forces as well as sealing upperworking chamber 46 from lower working chamber 48. Piston rod 34 isattached to piston assembly 32 and extends through upper working chamber46 and through an upper rod guide assembly 50 which closes the upper endof pressure tube 30. A sealing system seals the interface between upperrod guide assembly 50, reserve tube 36 and piston rod 34. The end ofpiston rod 34 opposite to piston assembly 32 is adapted to be secured tothe sprung mass of vehicle 10. Because piston rod 34 extends onlythrough upper working chamber 46 and not lower working chamber 48,extension and compression movements of piston assembly 32 with respectto pressure tube 30 causes a difference in the amount of fluid displacedin upper working chamber 46 and the amount of fluid displaced in lowerworking chamber 48. The difference in the amount of fluid displaced isknown as the “rod volume” and during extension movements it flowsthrough base valve assembly 38. During a compression movement of pistonassembly 32 with respect to pressure tube 30, valving within pistonassembly 32 allow fluid flow from lower working chamber 48 to upperworking chamber 46 and the “rod volume” of fluid flow flows throughcontrol valve 42 as described below.

Reserve tube 36 surrounds pressure tube 30 to define a fluid reservechamber 52 located between tubes 30 and 36. The bottom end of reservetube 36 is closed by a base cup 54 which is adapted to be connected tothe unsprung mass of vehicle 10. The upper end of reserve tube 36 isattached to upper rod guide assembly 50. Base valve assembly 38 isdisposed between lower working chamber 48 and reserve chamber 52 tocontrol the flow of fluid from reserve chamber 52 to lower workingchamber 48. When shock absorber 20 extends in length, an additionalvolume of fluid is needed in lower working chamber 48 due to the “rodvolume” concept. Thus, fluid will flow from reserve chamber 52 to lowerworking chamber 48 through base valve assembly 38 as detailed below.When shock absorber 20 compresses in length, an excess of fluid must beremoved from lower working chamber 48 due to the “rod volume” concept.Thus, fluid will flow from lower working chamber 48 to reserve chamber52 through control valve 42 as detailed below.

Piston assembly 32 comprises a piston body 60, a compression valveassembly 62 and an extension valve assembly 64. A nut 66 is assembled topiston rod 34 to secure compression valve assembly 62, piston body 60and extension valve assembly 64 to piston rod 34. Piston body 60 definesa plurality of compression passages 68 and a plurality of extensionpassages 70. Base valve assembly 38 comprises a valve body 72, anextension valve assembly 74 and a compression valve assembly 76. Valvebody 72 defines a plurality of extension passages 78 and a plurality ofcompression passages 80.

During a compression stroke, fluid in lower working chamber 48 ispressurized causing fluid pressure to react against compression valveassembly 62. Compression valve assembly 62 acts as a check valve betweenlower working chamber 48 and upper working chamber 46. The dampingcharacteristics for shock absorber 20 during a compression stroke arecontrolled by control valve 42 alone and possibly by control valve 42working in parallel with base valve assembly 38 as described below.Control valve 42 controls the flow of fluid from lower working chamber48 to upper working chamber 46 to control valve 42 to reserve chamber 52due to the “rod volume” concept during a compression stroke as discussedbelow. Compression valve assembly 76 controls the flow of fluid fromlower working chamber 48 to reserve chamber 52 during a compressionstroke. Compression valve assembly 76 can be designed as a safetyhydraulic relief valve, a damping valve working in parallel with controlvalve 42 or compression valve assembly can be removed from base valveassembly 38. During an extension stroke, compression passages 68 areclosed by compression valve assembly 62.

During an extension stroke, fluid in upper working chamber 46 ispressurized causing fluid pressure to react against extension valveassembly 64. Extension valve assembly 64 is designed as either a safetyhydraulic relief valve which will open when the fluid pressure withinupper working chamber 46 exceeds a predetermined limit or as a typicalpressure valve working in parallel with control valve 42 to change theshape of the damping curve as discussed below. The dampingcharacteristics for shock absorber 20 during an extension stroke arecontrolled by control valve 42 alone or by control valve 42 in parallelwith extension valve assembly 64 as discussed below. Control valve 42controls the flow of fluid from upper working chamber 46 to reservechamber 52. Replacement flow of fluid into lower working chamber 48during an extension stroke flows through base valve assembly 38. Fluidin lower working chamber 48 is reduced in pressure causing fluidpressure in reserve chamber 52 to open extension valve assembly 74 andallow fluid flow from reserve chamber 52 to lower working chamber 48through extension passages 78. Extension valve assembly 74 acts as acheck valve between reserve chamber 52 and lower working chamber 48. Thedamping characteristics for shock absorber 20 during an extension strokeare controlled by control valve 42 alone and possibly by extension valveassembly 64 in parallel with control valve 42 as described below.

Intermediate tube 40 engages upper rod guide assembly 50 on an upper endand it engages base valve assembly 38 on a lower end. An intermediatechamber 82 is defined between intermediate tube 40 and pressure tube 30.A passage 84 is formed in upper rod guide assembly 50 for fluidlyconnecting upper working chamber 46 and intermediate chamber 80.

Referring to FIG. 3, control valve 42 is illustrated in greater detail.Control valve 42 comprises an attachment fitting 90, a soft valveassembly 92, a valve assembly 94, a solenoid valve assembly 96 and anouter housing 98. Attachment fitting 90 defines an inlet passage 100aligned with a fluid passage 102 which extends through intermediate tube40 for fluid communication between intermediate chamber 82 and controlvalve 42. Attachment fitting 90 is axially received within a collar 104mounted on intermediate tube 40. An O-ring seals the interface betweenattachment fitting 90 and collar 104. Collar 104 is preferably adistinct piece from intermediate tube 40 and it is mounted ontointermediate tube 40 by welding or by any other means known in the art.

Attachment fitting 90, soft valve assembly 92, valve assembly 94, andsolenoid valve assembly 96 are all disposed within outer housing 98 andouter housing 98 is attached to reserve tube 36 by welding or by anyother means known in the art. Valve assembly 94 includes a valve seat106 and solenoid valve assembly 96 includes a valve body assembly 108.Valve seat 106 defines an axial bore 110 which receives fluid from softvalve assembly 92, valve body assembly 108 defines an axial bore 112 anda plurality of radial passages 114 which communicate with a return flowpassage 120 which is in communication with reserve chamber 52 through afluid passage 122 formed through reserve tube 36. An attachment plate124 is secured to outer housing 98 to position attachment fitting 90 andthe rest of the components of control valve 42 within outer housing 98.

Referring to FIGS. 2 and 3, the operation of shock absorber 20 will bedescribed when control valve 42 alone controls the damping loads forshock absorber 20. During a rebound or extension stroke, compressionvalve assembly 62 closes the plurality of compression passages 68 andfluid pressure within upper working chamber 46 increases. Fluid isforced from upper working chamber 46, through passage 84, intointermediate chamber 82, through fluid passage 102, through inletpassage 100 of attachment fitting 90, through soft valve assembly 92 asdiscussed below, to reach valve assembly 94.

The higher flow damping characteristics of shock absorber 20 aredetermined by the configuration of valve assembly 94 and solenoid valveassembly 96. As such, valve assembly 94 and solenoid valve assembly 96are configured to provide a predetermined damping function which iscontrolled by the signal provided to solenoid valve assembly 96. Thepredetermined damping function can be anywhere between a soft dampingfunction to a firm damping function based upon the operating conditionsof vehicle 10. At low piston velocities, control valve 42 remains closedand fluid flows through bleed passages that are made in piston assembly32 and base valve assembly 38. Shock absorber 20 thus operates similarto a typical double tube damper. At higher piston velocities, as fluidflow increases, fluid pressure against a plunger 126 of valve bodyassembly 108 will separate plunger 126 of valve body assembly 108 from avalve seat 128 of valve body assembly 108 and fluid will flow betweenplunger 126 of valve body assembly 108 and valve seat 128 of valve bodyassembly 108, through radial passages 114, through return flow passage120, through fluid passage 122 and into reserve chamber 52. The fluidpressure required to separate plunger 126 of valve body assembly 108from valve seat 128 of valve body assembly 108 will be determined bysolenoid valve assembly 96. The rebound or extension movement of pistonassembly 32 creates a low pressure within lower working chamber 48.Extension valve assembly 74 will open to allow fluid flow from reservechamber 52 to lower working chamber 48.

During a compression stroke, compression valve assembly 62 will open toallow fluid flow from lower working chamber 48 to upper working chamber46. Due to the “rod volume” concept, fluid in upper working chamber 46will flow from upper working chamber 46, through passage 84, intointermediate chamber 82, through fluid passage 102, through inletpassage 100 of attachment fitting 90, through soft valve assembly 92 asdiscussed below, to reach valve assembly 94.

Similar to an extension or rebound stroke, the damping characteristicsof shock absorber 20 are determined by the configuration of valveassembly 94 and solenoid valve assembly 96. As such, valve assembly 94and solenoid valve assembly 96 are configured to provide a predetermineddamping function which is controlled by the signal provided to solenoidvalve assembly 96. The predetermined damping function can be anywherebetween a soft damping function to a firm damping function based uponthe operating conditions of vehicle 10. At low piston velocities,control valve 42 remains closed and fluid flows through the bleedpassages that are made in piston assembly 32 and base valve assembly 38.Shock absorber 20 thus operates similar to a typical double tube damperat higher piston velocities, as fluid flow increases, fluid pressureagainst plunger 126 of valve body assembly 108 will separate plunger 126of valve body assembly 108 from valve seat 128 of valve body assembly108 and fluid will flow between plunger 126 of valve body assembly 108and valve seat 128 of valve body assembly 108, through radial passages114, through return flow passage 120, through fluid passage 122 and intoreserve chamber 52. The fluid pressure required to separate plunger 126of valve body assembly 108 from valve seat 128 of valve body assembly108 will be determined by solenoid valve assembly 96. Thus, the dampingcharacteristics for both an extension stroke and a compression strokeare controlled by control valve 42 in the same manner.

The fluid flow through and the damping generation characteristics forsoft valve assembly 92, similar to the fluid flow through and thedamping characteristics for valve assembly 94, are the same for both acompression stroke and a rebound or extension stroke. Soft valveassembly 92 comprises a valve body 130, a valve pin 132, an intake disc134, an orifice disc 136, a spacer 138, an upper spring seat 140, abiasing spring 142 and a lower spring seat 144.

Valve body 130 is disposed between attachment fitting 90 and valve seat106. An O-ring seals the interface between valve body 130 and attachmentfitting 90 and an O-ring seals the interface between valve body 130 andvalve seat 106. Valve body 130 defines a plurality of fluid passages 146and a central bore 148. Valve pin 132 extends through central bore 148.

Intake disc 134 and orifice disc 136 are disposed between valve body 130and valve pin 132 with orifice disc 136 engaging an annular land 150 onvalve body 130 to close fluid passages 146 and intake disc 134 beingdisposed between orifice disc 136 and valve pin 132. One or more bleedorifices 152 are defined by orifice disc 136 to allow a bleed flow offluid through soft valve assembly 92 as discussed below. While thepresent disclosure illustrates orifice disc 136 having bleed orifices152, it is within the scope of the present disclosure to have annularland 150 define bleed orifices 152. Assembled to valve pin 132 on theside of valve body 130 opposite to intake disc 134 and orifice disc 136are spacer 138, upper spring seat 140, biasing spring 142 and lowerspring seat 144. Lower spring seat 144 is secured to valve pin 132 tomaintain the assembly of soft valve assembly 92. Biasing spring 142urges valve pin 132 against intake disc 134 which is biased againstorifice disc 136 which is biased against annular land 150 on valve body130.

Soft valve assembly 92 provides for the tuning of damping forces at lowcurrent levels for solenoid valve assembly 96. Fluid flow flowing tosoft valve assembly 92 from inlet passage 100 of attachment fitting 90is directed to fluid passages 146. The initial fluid flow will flowthrough bleed orifices 152 to valve assembly 94 through valve seat 106.Fluid flow through valve assembly 94 is described above. As the fluidflow through bleed orifices 152 increases, the fluid pressure againstorifice disc 136 and intake disc 134 will eventually overcome thebiasing load produced by biasing spring 142 and orifice disc 136 willunseat from annular land 150 to open soft valve assembly 92. This fluidflow will also be directed to valve assembly 94 through valve seat 106.Tuning for soft valve assembly 92 can be accomplished by varying thesize and/or load of biasing spring 142, varying the thickness and/orflexibility of intake disc 134 and/or orifice disc 136, varying the sizeand/or number of bleed orifices 152 and varying the size and/or numberof fluid passages 146. The incorporation of soft valve assembly 92allows for the tuning or alteration of the shape of the damping curve atlow current levels to solenoid valve assembly 96 to adapt shock absorber20 to a specific vehicle performance. Because the pressure drop acrosssoft valve assembly 92 is very low at high current levels to solenoidvalve assembly 96 compared to the pressure drop across control valve 42,its effect on the damping characteristics is negligible.

As described above, soft valve assembly 92 allows for the tuning oralteration of the shape of the damping curve only at low current levelsto solenoid valve assembly 96. In order to change or alter the dampingcurve at high current levels to solenoid valve assembly 96, extensionvalve assembly 64 needs to be changed and compression valve assembly 76needs to be included.

If only control valve 42 controls the damping loads for shock absorber20, extension valve assembly 64 and compression valve assembly 76 aredesigned as hydraulic pressure relief valves or they are removed fromthe assembly. In order to tune or alter the damping curve at highcurrent levels to solenoid valve assembly, extension valve assembly 64and compression valve assembly 76 are designed as damping valves foropening at specific fluid pressures to contribute to the dampingcharacteristics for shock absorber 20 in parallel with control valve 42.

Referring now to FIG. 4, a soft valve assembly 192 in accordance withthe present disclosure is illustrated. Soft valve assembly 192 is adirect replacement for soft valve assembly 92 with soft valve assembly192 being disposed between an attachment fitting 190 and a valve seat206. Attachment fitting 190 is a direct replacement for attachmentfitting 90 and valve seat 206 is a direct replacement for valve seat106.

The flow through and the damping generation characteristics for softvalve assembly 192 are also the same for both a compression stroke and arebound or extension stroke. Soft valve assembly 192 comprises a valvebody 230, a valve pin 232, a plurality of intake discs 234, an orificedisc 236 and a valve retainer 238.

Valve body 230 is disposed between attachment fitting 190 and valve seat206. Valve body 230 defines a plurality of fluid passages 246 and acentral bore 248. Valve pin 232 extend through central bore 248.

Valve retainer 238, the plurality of intake discs 234 and orifice disc236 are disposed between valve body 230 and valve pin 232 with orificedisc 236 engaging an annular land 250 on valve body 230 to close fluidpassages 246. The plurality of intake discs 234 engage orifice disc 236and valve retainer 238 is disposed between the plurality of intake discs234 and valve pin 232. One or more bleed orifices 252 are defined byorifice disc 236 to allow a bleed flow of fluid through soft valveassembly 192 as discussed below. While the present disclosureillustrates orifice disc 236 having bleed orifices 252, it is within thescope of the present disclosure to have annular land 250 define bleedorifices 252.

Soft valve assembly 192 provides for the tuning of damping forces at lowcurrent levels for solenoid valve assembly 96. Fluid flow flowing tosoft valve assembly 192 from inlet passage 100 of attachment fitting 190is directed to fluid passages 246. The initial fluid flow will flowthrough bleed orifices 252 to valve assembly 94 through valve seat 206.Fluid flow through valve assembly 94 is described above. As the fluidflow through bleed orifices 252 increases, the fluid pressure againstorifice disc 236 and the plurality of intake discs 234 will eventuallyovercome the bending load for the plurality of intake discs 234 andorifice disc 236 and orifice disc 236 will unseat from annular land 250to open soft valve assembly 192. This fluid flow will also be directedto valve assembly 94 through valve seat 206. Tuning for soft valveassembly 192 can be accomplished by varying the thickness and/orflexibility of the plurality of intake discs 234 and/or orifice disc236, varying the size and/or number of bleed orifices 252 and varyingthe size and/or number of fluid passages 246. The incorporation of softvalve assembly 192 allows for the tuning or alteration of the shape ofthe damping curve to adapt shock absorber 20 to a specific vehicleperformance.

1. A shock absorber comprising: a pressure tube forming a fluid chamber;a piston assembly slidably disposed within said pressure tube, saidpiston assembly dividing said fluid chamber into an upper workingchamber and a lower working chamber; a reserve tube disposed around saidpressure tube; an intermediate tube disposed between said pressure tubeand said reserve tube, an intermediate chamber being defined betweensaid intermediate tube and said pressure tube, a reservoir chamber beingdefined between said intermediate tube and said reserve tube; and acontrol assembly mounted to said reserve tube, said control assemblyhaving an inlet in communication with said intermediate chamber and anoutlet in communication with said reservoir chamber, said controlassembly comprising: a first valve assembly disposed between said inletand said outlet; and a second valve assembly disposed between said firstvalve assembly and said outlet; wherein said first and second valveassemblies are in series between said inlet and said outlet such thatduring all fluid flow through said control assembly, all fluid flow fromsaid first valve assembly always flows through said second valveassembly; said first valve assembly includes a valve body, an intakedisc engaging said valve body and a first biasing member urging saidintake disc into engagement with said valve body; said second valveassembly includes a valve seat, a plunger and a second biasing memberurging said plunger into engagement with said valve seat; and fluidpressure in said intermediate chamber urges said plunger in a directionaway from said valve seat to separate said plunger from said valve seatto open said second valve assembly.
 2. The shock absorber according toclaim 1, wherein said second biasing member is a solenoid valveassembly.
 3. The shock absorber according to claim 2, wherein said firstbiasing member is a coil spring.
 4. The shock absorber according toclaim 1, wherein said first valve assembly defines a constantly openfluid passage between said first valve assembly and said second valveassembly.
 5. The shock absorber according to claim 1, wherein said valveseat of said second valve assembly defines an axial bore, fluid pressurein said axial bore urging said plunger in said direction away from saidvalve seat.
 6. The shock absorber according to claim 1, wherein saidvalve body of said first valve assembly defines a central bore, saidfirst valve assembly further comprising a valve pin extending throughsaid central bore, said first biasing member urging said valve pinagainst said intake disc to urge said intake disc into engagement withsaid valve body.
 7. The shock absorber according to claim 1, whereinsaid control assembly further comprises a seal directly engaging saidvalve body and directly engaging said valve seat.
 8. The shock absorberaccording to claim 1, wherein said control assembly further comprises anattachment fitting disposed between said first valve assembly and saidreserve tube.
 9. The shock absorber according to claim 8, wherein saidcontrol assembly further comprises a seal directly engaging said valvebody and directly engaging said attachment fitting.
 10. The shockabsorber according to claim 8, wherein said valve body of said firstvalve assembly defines a central bore, said first valve assembly furthercomprising a valve pin extending through said central bore, said firstbiasing member urging said valve pin against said intake disc to urgesaid intake disc into engagement with said valve body.
 11. The shockabsorber according to claim 10, wherein said valve seat of said secondvalve assembly defines an axial bore, fluid pressure in said axial boreurging said plunger in said direction away from said valve seat.
 12. Theshock absorber according to claim 11, wherein said control assemblyfurther comprises a seal directly engaging said valve body and directlyengaging said valve seat.
 13. The shock absorber according to claim 12,wherein said control assembly further comprises a seal directly engagingsaid valve body and directly engaging said attachment fitting.
 14. Theshock absorber according to claim 13, wherein said second biasing memberis a solenoid valve assembly.
 15. The shock absorber according to claim14, wherein said first biasing member is a coil spring.